In the oil-and-gas industry, blended fluid streams from wellheads or treatment processes must frequently be divided into separate streams of oil and water. However, blended fluid streams frequently have high pressures which must be reduced, both to protect downstream equipment and to improve the effectiveness of subsequent treatment processes. As an example, the fluid pressure from the wellhead depends upon the pressure of the reservoir. If the produced fluid stream is predominantly natural gas, the pressure may be 1,000 pounds per square inch (psi) or greater. Alternatively, if the produced fluid stream is predominantly oil, the pressure may be in the several hundred psi range.
Choke or control valves are conventionally used in the industry to regulate flow rates and fluid pressures. These valves can significantly reduce the pressure of a fluid stream. However, the pressure reduction corresponds to increased turbulence of the fluid stream flow. Oil and water droplets in the fluid stream may break apart due to the increased turbulence, causing the formation of oil-in-water or water-in-oil emulsions. Once formed, these emulsions are difficult to separate and can impair the performance of downstream treatment processes. In addition, smaller oil-and-water droplets, which are more easily dispersed in the fluid stream, are less likely to coalesce into larger droplets that can be separated.
If downstream oil-and-water separation processes are less effective, the oil stream may not meet the applicable standards for use. Similarly, the water stream may not meet the applicable standards for use, recycling, or disposal to a wastewater treatment plant or the environment. Alternatively, additional treatment steps or processes may be required, potentially increasing treatment costs, the types and quantities of chemicals used, and the amount of space needed to accommodate the process equipment. This may be a particular concern for off-shore applications, where space for equipment and storage is limited and transportation is difficult and expensive.
A need exists for a system that can achieve the required pressure drop while improving downstream oil-and-water separation. This improvement may be accomplished by reducing the shearing of oil or water droplets and the formation of tight oil-in-water and water-in-oil emulsions.